Central Florida Caterpillar Outbreak Ending, Says UF/IFAS Entomologist

Published: April 9th, 1996

Category: Environment, Florida, Research

GAINESVILLE—A University of Florida entomologist has reassuring words for Central Florida homeowners who see a caterpillar carpet when they look out at their yards: The fuzzy visitors will be gone in a few more weeks.

An outbreak of forest tent caterpillars in several Central Florida counties has had many homeowners worried, said Professor John Foltz, an entomologist with UF’s Institute of Food and Agricultural Sciences.

Will the leaf-eating caterpillars kill the trees on which they feed? Are they a threat to people? Should pesticides be used to control the caterpillar? The answer to all these questions is no, Foltz said.

While some areas in Central Florida are literally crawling with the caterpillars, the outbreak appears to be ending, Foltz said. In fact, the population appears to be harboring a virus that is doing a better job of killing off the caterpillars than insecticides would.

“The forest tent caterpillar is really a people problem rather than a biological problem,” Foltz said. “Trees will survive, even after two years of feeding by the caterpillars, unless other stress agents are involved, like drought or flood.

“In the forest environment, it’s not much of a tree problem, but in an urban environment, when it strips an oak of its leaves and moves on, there’s little that it doesn’t eat.”

Joanne Hoffman, a program assistant in the Hillsborough County extension office, said so many calls about the caterpillar were coming in that Hillsborough set up an answering machine to handle callers’ questions. At least 500 calls were logged in about two weeks, she said.

Entomologist James Meeker, of the Florida Division of Forestry, traveled to Central Florida in February to do an egg mass survey of the insect. From the survey, he forecast widespread defoliation this spring but said the virus has caused a rapid reduction in the caterpillars.

“Everybody and his mother noticed them last year,” Meeker said, “but the caterpillars now appear to be nearing the end of their life stage.”

Foltz said homeowners’ concerns are real. The caterpillars can crawl up walls and into houses that are not well sealed. Caterpillar frass, or droppings, can cover cars, patios, pools and anything else during a heavy infestation. The caterpillars that are dying from the virus bloat and leave coffee-colored stains.

The caterpillars that live will spin cocoons, which will spread yellow powder everywhere. The moths may swarm around light bulbs for a while but only live a few days.

In the South, the caterpillars prefer to dine on oaks, water tupelo, sweetgum, blackgum, cottonwood and elms, but will expand their palate to include other foliage after they have left their favorite hosts bare of leaves.

“This outbreak is in its fourth year and people are concerned about whether it is going to last forever,” Foltz said. “This outbreak, however, appears to have reached its high point in its third year and is collapsing this year. In the next few weeks, there will be fewer cocoons and, later in the month, fewer moths.”

Foltz said the forest tent caterpillar is as widespread as any forest defoliator in North America but outbreaks are not frequent. The only other outbreak in recorded history in Florida was in the 1960s in Marion, Citrus, Pasco and Hernando counties.

Meeker and Foltz said it’s too late in this outbreak for insecticides. Spraying a rose bush, for example, might result in killing each caterpillar that takes a bite, but if a thousand caterpillars take a bite the spraying wouldn’t be effective anyway.

Homeowners and gardeners worried about tree mortality should wait until mid-summer before removing any apparently dead trees. Insect defoliation alone rarely kills hardwood trees. A tree with dead lower branches will often recover if given appropriate water, nutrition and protection from other pests.

Meeker said squashed caterpillars leave quite a mess and said old-fashioned patience might be the best cure for the problem. If the caterpillars are allowed to wander around and pupate, they’ll change into much less bothersome moths in a few weeks.

“I’d advise people to be patient and, if at all possible, view this as an educational opportunity. This is interesting because it hasn’t happened down there before. This can be learned from and appreciated,” Meeker said.

“In a couple of weeks time, people will be sitting out on their porches at night and noticing a whole lot of moths and may not make the connection between the moths and the caterpillars,” Meeker said. “After this event, who knows if an outbreak will occur in these people’s lifetimes again.”

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Cindy Spence

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